Regional groundwater resource modelling using modflow - a case study

Abstract

Water is the basic need for all living organisms and is essential for sustainable development. World is facing a growing demand for high quality water resources while the water availability remains constant. Quantifying the water resources is necessary for efficient use of water resources. Groundwater modelling is a tool used to study the groundwater behavior and quantify the groundwater resource. In this study, Visual MODFLOW was used to study the groundwater behavior and predict groundwater heads at different scenarios in West Godavari district. Andhra Pradesh is known as ‘Rice bowl of India’. East Godavari and West Godavari districts contribute to the maximum production of paddy in Andhra Pradesh. Around 3000TMC of Godavari river is draining into bay of Bengal, whereas flow in Krishna River is in a critical condition. So, Government of Andhra Pradesh planned to divert surplus water in Godavari river to Krishna river using ‘Pattiseema lift irrigation project’. Pattiseema lift irrigation project will pumping around 100 -125 TMC using 24 motors to Godavari river. The main objective of the study is to analyse the spatial and temporal variation of groundwater, identifying the potential groundwater zones to collect the lithology and developing the groundwater flow model for the study area were the different objectives of the study. Spatial and temporal variation of the groundwater heads was studied using a plot between groundwater heads at different locations with respect to time and observed that groundwater vary with respect to topography, climate and soil properties. Potential groundwater zones were identified by developing map using groundwater heads. Different locations were selected and well log was collected from Groundwater and Water audit Department, Government of Andhra Pradesh. From lithology data, it is observed that major portion of the West Godavari district was occupied by sandstone followed by clay, sand, clayey sandstone, granite gneissis and shales. Model is developed using data from 53 head observation wells from 2003 to 2017. A model was developed by assigning all boundaries, aquifer properties and head observation levels. Calibration and validation of the model was done. The model has been used for prediction with different scenarios and also used to study the groundwater behavior at different scenarios. Model was also used to study the effect of ‘Pattiseema lift irrigation project’ on groundwater recharge. After assigning all inputs, the model was calibrated with 2003 to 2005 year data in steady state condition with and 2006 to 2011 data was added for transient state condition. Calibrated model was validated using groundwater heads up to 2017. In validation a new recharge layer is added considering the effect of lift irrigation canal. Validated model was used for prediction. In prediction the effect of decreasing recharge by 5 per cent in every five year for the next fifteen years was studied. The effect of increasing the pumping rate by 5 per cent in every five year for the next fifteen years was also studied. The effect of ‘Pattiseema lift irrigation project was also studied and we observed that considering the lift irrigation project there was an increase in the net recharge from 50 mm/year to 100 mm/year. There was also a 3 m rise in groundwater level nearer to the canal From this study, it was observed that West Godavari district is safe with increase in pumping rate and decrease in recharge up to 2032. This is due to the recharge from rivers and lift irrigation canal. Considering the predicted heads and surface water availability, proper cropping pattern can be adopted to increase productivity. Conjunctive use of surface and groundwater can also be adopted in the study area to solve the water shortage problem. A better understanding of the behavior of the groundwater resources of the area can help in making efficient managerial decisions in future.